1. Field of the Invention
This invention relates to toasters of the type having a double wall structure permitting the outer walls to remain relatively cool during operation of the toaster. In particular, it concerns improved free convective cooling of these walls by addition of a member for inward deflection of the column of hot air rising from the toasting chamber.
2. Description of the Prior Art
The hazards of working with hot appliances are well known and while surface temperatures can be measured with a fair degree of accuracy, the response of individuals when contacting surfaces at various temperatures is a highly subjective one. Nonetheless, on the basis of appropriate studies, practical guides--e.g., Underwriters Laboratory Bulletin #1005 for electric irons--have been developed presenting standards for normal (continuous contact and short term (momentary) contact with hot materials of various types. In particular, on the basis of values from the cited bulletin and an ambient air temperature of 77.degree. F. (25.degree. C.), for metallic members the maximum surface temperatures under these conditions are established as 131.degree. F. (55.degree. C.) and 140.degree. F. (60.degree. C.), respectively. Contrastingly, from non-metallic members the same bulletin indicates 167.degree. F. (75.degree. C.) and 185.degree. F. (85.degree. C.) as the maximum temperatures under the same contact conditions.
Because of the above-mentioned factors, there is interest in ways by which the temperatures of appliance surfaces which users may contact can be reduced to values well below these maxima. This is particularly true of appliances such as the common automatic toaster, where one approach--known from U.S. Pat. No. 2,476,142--is to use a double-walled structure with cooling air flowing through the space between the outer and inner walls. This patent shows a toaster having an outer, non-metallic (thermoplastic) cover or "housing" and an inner, metallic reflector shield slightly spaced from the cover to form a cooling space between them. Vents at the bottom and top of the cover permit continuous flow of air through the space. The shield, disposed between the heating elements and the cover, serves to reflect and absorb heat radiated by the elements.
Heat absorbed by the shield is transferred to the air in the cooling space, causing it to move upwardly by free convection and carry this heat away. The cover therefore remains at a temperature low enough to allow touching as well as to bar softening of the thermoplastic cover material. According to this patent, however, bread is fed laterally through the toaster and thus two large openings are provided at opposite ends of the toaster, which openings contribute significantly to lowering the internal temperature. When this teaching of a "double-wall" with an exhaust vent at the top of the cover is applied, however, to toasters having a chamber with a top opening through which bread is lowered for toasting and through which it is raised upon completion of the toasting--there being no lateral openings through which the bread (and the air) can move--we have found that the cover temperatures increase, an obviously undesirable result.
It is also known to vent the toasting chamber directly--e.g., U.S. Pat. No. 2,414,325--which also shows a heating control and a draft controller for making melba toast, the heat and draft both being reduced, causing the bread to be thoroughly dried and its surface browned. Such direct venting of the toasting chamber is also known from U.S. Pat. No. 2,071,234 which shows a toaster with an electrically-heated central core about which bread slices can be disposed in separate toasting "pockets" and having air inlets at the sides of the pockets and outlets in the top of the outer wall. The latter patent includes a duct arrangement for recirculating the convection air currents at high temperatures for contact with the surface of the bread being toasted, the purpose being to achieve greater toasting efficiency. Such recirculation inherently results in higher temperatures for cover portions near the exit of the toasting chamber. Thus, there is a need for improved air cooling of toaster covers.